Work Stream 8: Thermoplastic in Situ Polymerisation (TPIP) and Double Diaphragm Forming (DDF) for Moulding of Complex Parts at Scale

This project brings together expertise in in-situ moulding at the University of Edinburgh with expertise in forming at the University of Nottingham and builds on a previous Feasibility Study on integration of thermoplastic in situ polymerisation (TPIP) with double diaphragm forming (DDF).

Very low viscosity (~10 cP) monomers combined with double diaphragm forming (DDF) presents a novel opportunity to create huge (multi-metre e.g., wind turbine, train body panels) thermoplastic structures. DDF facilitates filling before forming; the initially flat reinforcement is easier to infuse due to more consistent permeability and the presence of the liquid provides lubrication to reduce inter-ply friction during forming. Furthermore, pot life can be extended through thermal control (Infusion can be undertaken at temperatures at which polymerisation rates are minimal) and no temperature cycling is required – polymerisation occurs below the final polymer melt temperature, so the component is immediately solid, and no cooling step is needed.

With increasingly pressing sustainability goals in all sectors, thermoplastic composite manufacturing developments are timely. Low cost, low emission processes are needed to create recyclable components that meet stringent regulations.  The recently finished Feasibility Study established the basic process, determining processing parameters and de-risking manufacturing. This successor project will develop the technology to make parts with realistic geometries, using the new ‘tea tray’ DDF tooling at the University of Nottingham. It will demonstrate the ability to achieve effective forming using low viscosity resins and tie that to software developments in conjunction with ESI.   The DDF tool at the University of Nottingham is based on the tool at the AMRC and so the development pathway is streamlined. Using this link, the project can establish key components of the process (frame design, injection system requirements, drying, manufacturing window) to take this to TRL 3, before translating to the catapult. The DDF matched tool provides an easily controlled temperature cycle at a medium scale to establish and de-risk the process before progressing to a larger, single sided double diaphragm tool using non-contact heating. The University of Nottingham have a small-scale double diaphragm former and the AMRC have a much larger version (3 x 1.8 m), so there is an available pathway to progress to larger parts without the need for matched tooling. The process also enables the introduction of remouldable resins, thus facilitating the transformation of composite manufacture into a circular economy and reducing disposal to landfill.

Objectives 

• Assemble low-viscosity diaphragm forming system
  In conjunction with AMRC (in an advisory role), develop the existing double diaphragm tooling at UoN to incorporate a bespoke frame suitable for a low viscosity resin system. Integrate with the UoE mixing system. Specific clamp design elements will be required to ensure minimal bridging at the edge to prevent racetracking during fill.
• Establish forming model 
  In conjunction with ESI, build on a basic model of the fill-form process using the PAM software suite to represent the tea tray geometry. Demonstrate virtually the benefits of
  the low viscosity (fast fill, lubrication) or waxy (high tack, resistance to corner thinning) resin on shear behaviour during forming in terms of fibre angle, wrinkling and corner thinning, and validate experimentally.
• Establish processing method
  Produce tea tray component in double diaphragm tool utilising one-stage fill and form, and two-stage quench and form. Ensure reproducibility and establish appropriate processing window.
• Quality assessment and validation of model 
  Use metrology-grade 3D laser scanner (Creaform) and Apodius Vision System facilities to capture forming behaviour, distortion, fibre angle and wrinkles and correlate with model (Objective 2). Assess quality of the parts in terms of thermomechanical behaviour and microstructure.